Tanioka, T., Matsumoto, K., 2020. Stability of marine organic matter respiration stoichiometry. Geophysical Research Letters 47, e2019GL085564.

https://doi.org/10.1029/2019GL085564 Abstract: The amount of oxygen consumed during organic matter remineralization critically depends on how much organic carbon is remineralized per unit dissolved oxygen respired (respiratory quotient, RQ) but the global distribution and the mechanisms that control RQare not well understood. Here we estimate RQ in the surface ocean by using two independent methods, one using satellite-derived macromolecular composition of phytoplankton and another using objectively gridded nutrient data. Both methods yield mean RQ of ~0.7 with small spatial variability consistent with previous estimates. This pattern is likely to be a result of phytoplankton protein content universally exceeding those of carbohydrates and lipids. At face value, the relative stability of RQ suggests that the remineralization stoichiometry will not affect the ongoing deoxygenation of the world ocean. However, the possibility remains that RQ may increase in the future (e.g., organic matter becoming more carbohydrate-dominated) and thus ameliorate deoxygenation. Plain Language Summary: Most organic carbon produced by phytoplankton in the surface ocean is decomposed by bacteria using dissolved oxygen. This process is expected to accelerate under global warming leading to a significant loss of oxygen from the marine ecosystem. In order to accurately estimate the total amount of oxygen consumed during the decomposition of organic matter, we require information on how much organic carbon is respired per unit of oxygen consumed (respiratory quotient). Here we estimate respiratory quotient using two independent methods and demonstrate that the estimates agree in showing a nearly uniform value in large parts of the world ocean. We suggest that this is attributable to the fact that globally, the organic matter is largely made of protein which requires more oxygen than other molecules such as lipid and carbohydrate.

Tao, H., Qiu, Z., Ji, H., Qiu, J., Allen, M.B., 2020. An integrated approach to understanding the depositional environment and organic matter enrichment factor in Carboniferous source rocks, Junggar Basin, NWChina. Geological Journal 55, 31-43.

https://doi.org/10.1002/gj.3353 13 Multiple indicators (trace fossils, trace metals, and δ C ) are used to assess the depositional environments and org controls on organic carbon accumulation in the Lower Carboniferous Nanmingshui Formation, Junggar Basin, Nereites NWChina. The majority of trace fossils belong to the ichnofacies, representing low energy, oxygen- Planolites poor, and relatively quiet bottom water environments. However, the shallow water trace fossil also appears in the strata, possibly reflecting variations in the bottom water oxygen contents of the turbidite succession. Redox proxies Th/U, V/Sc, and V/(V + Ni) reveal variable redox conditions; most of the samples are in the range from suboxic to anoxic depositional conditions. Ni and Cu show a positive correlation with TOC, but U and V have no correlation with TOC, also suggesting the redox conditions were mainly suboxic. The P/Al and Cu/Al ratios of all samples are higher than those of Post-Archean Australian Shales (PAAS), and about two-thirds of the samples' Ba/Al and Ni/Al ratios are close to or higher than PAAS, suggesting the Early 13 Carboniferous Junggar Basin had relatively high palaeo-productivity levels. δ C values average - 23.75‰, org reflecting a mixture of terrestrial organic and marine organic matter. The indexes of Ba/Al, Cu/Al, Ni/Al, and 13 δ C show good positive correlations with TOC, indicating the palaeo-productivity played an important role org for the organic matter accumulation. On the other hand, the TOC correlates inversely with redox proxies (Th/U, V/Sc, and V/(V + Ni)), suggesting the preservation conditions (anoxia) are not the control factor of organic matters accumulation. Using these multiple approaches, our results indicate that productivity was the primary factor controlling organic matter accumulation.

Tarnas, J.D., Mustard, J.F., Lin, H., Goudge, T.A., Amador, E.S., Bramble, M.S., Kremer, C.H., Zhang, X., Itoh, Y., Parente, M., 2019. Orbital identification of hydrated silica in Jezero crater, Mars. Geophysical Research Letters 46, 12771-12782.

https://doi.org/10.1029/2019GL085584